Art of mounting piezoelectric crystals



June a, 1943. A, OKOVQY 2,321,358

ART OF MOUNTING PIEZOELECTRIC CRYSTALS Filed June 30, 1941 Snventor Wzaw Patented June'8,

, an'ror MOUNTING rmzonnacraic cars'rans Samuel A. Bokovoy, Audubon, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application June 30, 1941, Serial No. 400,451

6 Claims.

This invention relates to the art of mounting piezoelectric crystals and, though not limited thereto, has special reference to the mounting of so-called thickness-mode quartz crystals.

It has heretofore been proposed to make the necessary two electrodes for "thickness-mode" and contour-mode" piemelectric crystals in the form of adherent metalliccoatings or films applied directly to the surface of the crystal.

Heretofore, such metalized crystals" have been mounted either by the application of a clamping force applied at opposite points along a nodal axis of the crystal or by a pair of clamps which engage both major surfaces of the crystal adjacent the opposite ends thereof. In the former case, the crystal may move as on a pivot and the resulting friction may wear away the thin metal films, whereas in the latter case the application of a clamping force to the major or electrode surfaces over a substantial. area adjacent the ends thereof may inhibit maximum oscillatory movement of the crystal.

Accordingly, the principal object of the present invention is to obviate the foregoing and other less apparent objections to prior artmountings for metalized crystals.

I Another and important object of the present Figure 3 is a side elevation and Figure 4 an end elevation of another crystal holder embodymg the invention,

Figure 5 is a top plan view, and Figure 6 a side elevation of a duplex crystal holder incorporating the invention.

In Fig. 1.0 designates an oblong crystal element or plate. or bar possessing piezoelectric properties and which may be constituted of quartz, tourmaline or Rochelle salts. This crystal is provided with a pair of electrodes .1 and 2 which, as shown, preferably -comprise adherent foil-like or integral film like coatings or silver or other suitable metal. These electrodes partially cover the two major faces of the crystal and extend over the edges of the crystal at its end zones la, 20. and cover the invention is to provide a simplified, inexpensive a and trouble-free pressure-type .mount for metalized piezoelectric crystals, and one requiring the minimum of skill in the assembly and ."adjustment of its parts.

The foregoing and other objects are achieved in accordance with the present'invention by ex-. tending the usual metal electrode coatings beyond the electrode or major surfaces of the crystal so that they at least partially cover certain of the minor surfaces thereof, and by applying the clamping force to the said .metaliaed minor surfaces, or totheme'talized right angled or beveled edges defining the boi'mdaries of the said major and minor crystal faces, rather than to the major surfaces, per se. The clamping minor side and end faces of the element within these zones. Since each coated minor side-face of the crystal is electrically connected to a metalized major face the metal on the minor end-faces lb and 2b of the crystal may be I omitted or erased, if desired.

The crystal 0 is supported in accordance with I the invention, preferably intermediate its ends by a pair of clamping elements 3 and 4 (later described) which exert their clampin force upon the metallized minor faces la, 2a of the crystal (as shown more clearly in Fig. 2) or upon the edges of the crystal which define the boundary between its major faces and its minor side faces, (as shown in Figs. 4 and 5). In this later case the said edges of the crystal may be beveled as indicated at c, Fig. 4. l

The supporting clamps 3 and 4 (Figs. 1-4) are constructed and positioned, in accordance with v the invention, to permit of accurate and rapid mounting and replacement of a crystal by an unskilled operator, and to this end comprises expansible rings (Figs. 1'4) or jaws (Figs. 5 and 6) constituted of spring metal. Thus, as shown in Figs.. 1 to 4, inclusive, each clamp may comprise a spring metal strip which is secured at one end to the insulating base 5 of the holder as by means of a metal stud or screw 6 and a somewhat narrower free end 1 which is bent-around the crystal C and extends through an elongated slot g struck out from the strip adjacent its fixed end it. The slotted portion. of the strip extends a sufficient distance above (or at a right angle to) the base 5 to provide a clearance space between the surface of the base and the bottom of the loop. Thus, the

clamp may be expanded to permit the crystal C to be entered therein simply by pressing the free end 9 I r downwardly or inwardly m the direction of the base.

In accordance with the principle of' the invention the clamping force is confined to the minor side faces of the crystal or to the side edges thereof and is not applied to its major surfaces. Accordingly, referring particularly to Fig. 2, when the mounting force is to be applied to the minor side fac'es of the crystal the spring metal loops or clamps may be flattened at the area indicated at i,'where it contacts the said faces of the crystal and is bowed outwardly, as indicated at p, away from the major faces of the crystal.

Where, as shown in Fig. 4, the clamping force is to be applied to the edges of the crystal, the loop may be bowed outwardly away from both the major faces and the minor side faces of the crystal so that its clamping force is confined to the said edges. As previously set forth, andas shown at c, Fig. 4, theedges of the crystal C to which the clamping force is applied ma be beveled, if desired.

The duplex holder shown in Figs. and 6 is designed to support two metalized oblong plano-convex'crystals Ci C2, respectively, on opposite sides of an insulating upright I which is' provided for the purpose on a socket base 5. The clamping members, which are here designated 8, 9, l0 and II, respectively, instead of being in the form of loops or rings are of U-shape construction and are secured at the base of the U to the upright support I by means of screws Ill. The legs -of these U-shape members extend outwardly at an obtuse angle with respect to the base, and then inwardly toward each other, preferably at a right angle, as indicated at r, Fig. -5. The clamping force is applied to the crystals along their metalized edges by the angularly disposed legs of these' flexible clamps. In order to prevent longitudinal movement of the crystals in either direction a- What is claimed is:

1. In combination, a piezoelectric crystal having major and minor faces, a metal coating on each major face ofv said crystal and comprising a pair of electrodes therefor, said metal coatings extending over the edges of said crystal and partially covering the minor faces thereof, and means for applying a clamping force to said crystal contiguous only said extended portions of said metal coating, said clamping means comprising a spring metal member which surrounds said crystal and is bowed outwardly out of contact with its said metal covered electrode and faces.

. 2. In combination, a piezoelectric crystal having major and minor faces, a metal coating on each major face of said crystal and comprising a pair of electrodes therefor, said metal coatings extending over the edges of said crystal and partially covering the minor faces thereof, and means for applying a clamping force to said crystal contiguous only said extended portions of said metal coatings, said clamping meanscomprising a substantially U-shape member constituted of spring metal and having inwardly bent legs between which said crystal is adapted to be seated. 3. In combination, an oblong piezoelectric crystal, a metal coating on each major face of'said crystal and comprising a, pair of electrodes therefor, said metal coatings covering the long edges of said crystal, and means for applying a clamping force to said metal covered edges of said crystal.

44 The invention as set forth in claim 3 and wherein said long edges of said crystal are beveled and said clamping force is applied-to said meta on, said clamps being shaped to contact said crys- -tal adjacent only the said metalized minor faces thereof. 1

6. A holder for a piezoelectric crystal having metalized edges at least partiall defining the metalized edges thereof.

SAMUEL A. BOKOVOY. 

